It used to be that the network which controlled your telephone was different than the network which controlled your computer. In the not-too-distant future, these two networks will become one. For example, so-called “IP telephones” (short for “Internet-Protocol telephones”) will be able to function much like conventional telephones, albeit using unconventional means. That is, IP telephones and other network-based systems will be connected to a network capable of sending and receiving both voice, data and other signals (i.e., video) as Internet-Protocol signals.
Separate from the type of information these systems will handle is the issue of how to provide power to them.
One way to provide power is to use an electrical outlet. This connects a system to the electric company's power grid. A second method is to provide power using the same physical conductors (e.g., wires) which handle voice or data information. That is, power supplied by the network itself. This is a more traditional method.
Additional methods have also been proposed, all of which use conductors within a network cable which is used to connect a system (e.g., IP telephone,) to the network.
For example, a conventional “local area network” (“LAN”) cable which connects an IP telephone to a network contains eight wires. Of the eight wires, four are typically used to transmit and receive voice and data information. These four may also be used to supply power if power is to be supplied over the same wires (i.e., the second method mentioned above) which are providing voice and data information. As is known in the art, this is not always the best way to provide power. Many times it is too complicated to place power on the same wires as data and still preserve the integrity of the data.
Alternatively, the remaining four extra or spare wires may be used to supply power only.
Specifically, a third method suggests that network-based systems be powered by placing two signals (e.g., voltages) each of opposite polarity (e.g., +V, −V) on two of the remaining four wires. This method is referred to as a “differential mode” or “differential voltage” technique via one pair.
The fourth suggested method uses all four of the remaining wires. In this method the same nominal voltage, (i.e., either +V or −V) is placed on two of the remaining wires while a second nominal voltage of opposite polarity is placed on the remaining pair of wires. This method is referred to as a “common mode” or “common voltage” technique via two pairs.
Some network-based systems or devices (hereafter collectively referred to as “network-based device”) have been developed which are adapted to be powered using the third method mentioned above. Other network-based devices are being developed which can only be powered using the fourth method just discussed.
It is desirable, however, to provide network-based devices which are capable of operating when power is supplied using either method.
Other desires will become apparent from the drawings, detailed description of the invention and claims which follow.